1. Field of the Invention
The invention refers to a star-delta-switch with a rotatable switch-shaft having a camshaft portion with cams for closing and, by this, closeable circuit-breaking contacts, delta-connection contacts and star-connection contacts which are closeable before the delta-connection contacts and a switch mechanism controlling the rotation of the switch-shaft.
2. Description of the Prior Art
In known star-delta switches, control of the contacts is effected solely by rotation of the camshaft. This has the disadvantage that, by quick operation of the switch for switching from the delta-connection position to the off-position, the time is not sufficient to extinguish the resulting arcs before the star-connection contacts close, whereby short circuits may occur. That is the reason why no-voltage release devices have very rarely been used with known star-delta-switches.
A star-delta-switch with a no-voltage release device has been proposed, but its construction is very expensive. This known switch has a ratchet clutch which connects a switch-shaft with cams operating the star-connection contacts, which permits these cams to be rotated with the switch-shaft only in the direction of turning-on. When the switch is turned off, these cams are not taken along so that a closure of the star-connection contacts cannot occur. The disadvantage of this known switch is its complicated construction, caused by the ratchet clutch.
It is also possible to switch from the delta-connection position to the star-connection position but this causes the opening of the circuit-breaking contacts so that a motor connected to the circuit comes to a standstill. When without switching into the off-position first, the switch is turned back into the delta-connection position, the circuit contacts are closed and the motor is started directly in the delta-connection.
A control switch with an axially displaceable, spring-biased shaft connected to cams is known but this switch is not a star-delta-switch but is useful only for switching from one switching position to an adjacent one. Therefore the cams of said known control switch are provided with control surfaces for each of the axial working positions of the cams with regard to the switch-bridges, said control surfaces taking effect during twisting said cams to handle in each of said axial working positions a switching program.